Sity electrical pulses to crystal



June 1954 H. c. TORREY ET AL ,0 4 I APPARATUS FOR APPLYINGHIGH-INTENSITY ELECTRICAL PULSES T0 CRYSTAL RECTIFIERS Filed Jan. 15,1946 FIG. 3

TIME

aw f (9 INVENTORS HENRY C. TORREY JEROME B. WIESNER ATTORNEY PatentedJune 22, 1954 APPARATUS FOR APE'LYING HIGH-INTEN- SITY ELECTRICAL PULSESTO CRYSTAL RECTIFIERS Henry C. Torrey, Cambrid B. Wiesner, Dearborn,

ge, Mass, and Jerome Mich, assignors, by

mesne assignments, to the United States of America as represented by theSecretary of the Navy Application January 15, 1946, Serial No. 641,351

8 Claims.

This invention relates to electrical test equipment and moreparticularly to apparatus capable of subjecting various types ofelectrical apparatus to a high intensity electrical pulse ofpredetermined energy content.

Subjecting electrical equipment to electrical surges involvesspecialized apparatus, the design of which depends upon the particularequipment to be subjected to the electrical surges. The principles ofthe present invention are herein disclosed in connection with thelaboratory and production testing of cartridge-type crystal rectifiers.

In the. manufacture of cartridge-type crystal rectifiers, numerous andextensive tests are made before the unit is marketed, which tests resultin a substantial increase in total cost. In pulsed radio frequencysystems, impairment and failure of the crystal is usually caused by theapplication thereto of a voltage pulse or spike of very short timeduration, often less than 0.01 microsecond. In such a short time, thecrystal and the whisker contactor are unable to conduct the dissipatedheat away from the contact. It has been observed'that the resultingtemperature is essentially proportional to the total energy in the spikerather than its peak power. For this reason, if a pulse energy test ismade before the other required tests, the unit cost of manufacture canbe considerably decreased and the crystal reliability increased.

An object of this invention is to provide a device for applying pulseenergy to a cartridge-type crystal rectifier or similar electricalequipment.

Another object of this invention Is to provide a device for applyingpulse energy to a cartridgetype crystal rectifier of simple mechanicalconstruction, efiicient operation and which is readily maintained.

These and other objects will be apparent from A a careful considerationof the specification and the accompanying drawings in which:

Fig. 1 is a longitudinal,cross-sectional view of a preferred embodimentof the present invention;

Fig. 2 is a graph showing certain voltage-time relationships existing inthe apparatus of Fig. 1; and

Fig. 3 is a cross-sectional view taken along axis 3-3 of Fig. 1.

Referring more specifically to the drawings, IS

Fig. 1 shows a coaxial line Ill, of length I, whose characteristicimpedance is substantially equal to the impedance of the crystal to betested, and which consists of a substantially cylindrical outerconductor II externally threaded at one end, and

7 polished. A dielectric sleeve I 1,

an inner conductor I2. Two insulating bushings I8 and 28, similarlyconstructed, are secured within outer conductor II by small dielectricpins 26 placed in small holes drilled through outer conductor II andinto bushings I8 and 28, as shown in Fig. 3. These bushings I8 and 28slidably support and electrically insulate the inner conductor I2.Bushing I8, located near the un-- threaded end of outer conductor II,also acts as a stop for inner conductor I2 and thus, an adjacent metalflange I3 is silver soldered to outer conductor I I for further support.An internally threaded metal cap 24. which engages the correspondinglythreaded end of outer conductor II, is drilled at its center and fittedwith end fingers 21 to releasably hold a cartridge-type crystalrectifier 3B. The crystal cartridge 30 has a metal base Si and a metalprong 33 separated and insulated by a ceramic case 32 which also housesthe crystal and the contacting whisker. The end fingers 2'! hold theceramic case 32 in such a manner that the metal base 3I and the outerconductor II are in electrical contact and the metal prong 33 extendscentrally into the outer conductor II. A metal sleeve 23 is attached tothe prong 33 of the crystal cartridge 38 by fingers 29 extending fromone'end of the sleeve. A fiat metal contact 22 is soldered to the end ofsleeve 23 opposite the fingers 29. The fingers 29 fit securely over theprong 33 to provide good electrical contact thereat. A contact I4,hernispherically shaped to minimize capacity and high potentialgradients, is fitted into the end of inner conductor I2 adjacent tothe'flat contact 22 and secured by a metal contact plug I9. The contactsI4 and 22 have a metal base and are covered with a very hardshock-resistant material, such as osmium-rhodium, which is ground andinternally threaded at both ends, mechanically connects and electricallyinsulates a core rod or plunger I5 of a solenoid 43 from inner conductorI2. Thus, the core rod [5 threaded at one end thereof engages a metalcoupling I6 which is in turn threaded and engages one end of thedielectric sleeve IT. A metal plug 2|, externally threaded, which slidesover the end of inner conductor I2 and silver soldered thereto, screwsinto the other end of the dielectric sleeve IT. The inner conductor I2and the coupling I6 are electrically connected by a resistor 25 and ahelical spring 20 located inside the dielectric sleeve I1, the resistor25 being soft soldered at one end to the plug 2I, and in contact at theother end with the helical spring 20 which in turn is soldered to thecoupling I6.

In actual operation the device is usually vertically mounted with corerod l at the top. A solenoid 43 is energized causin core rod l5 andinner conductor [2 to rise a predetermined distance. The metal sleeve 23is fitted over the metal prong 33 of crystal cartridge 38 and thislatter assembly inserted into the end fingers 21 of the cap 24 so thatflat contact 22 is directly beneath and in line with hemisphericalcontact M. The coaxial line is charged to a voltage V by connecting avoltage source 44 directly to outer conductor II and indirectly to innerconductor l2 through resistor 25. Resistor has a very high resistancevalue limiting the output current from the voltage source '44 duringdischarge and making the upper end of coaxial line !0 appearopen-circuited. When the solenoid 43 is deenergized, inner conductor l2drops very rapidly, initially to prevent field emission, engages contactI4 and 22, forces crystal cartridge from the end fingers 21 of the cap24 and final ly comes to rest when plug 2| meets dielectric bushing 18.When contacts I4 and 22' are engaged the energy stored in coaxial line10 is discharged through .and absorbed by the crystal in crystalcartridge 30.

It is generally known that when a uniformly charged transmission line isdischarged at one end into a load which has the same impedance as thecharacteristic impedance of the line, a pulse of electromagnetic energywill flow at a voltage equal to one-half the voltage across the line fora period of time equal to twice the length of the line divided by thevelocity of the wave in the line.

The wave shape shown in Fig. 2 is that which would be obtained from anideal match between the characteristic impedance of line Iii and theimpedance of the crystal in crystal cartridge 30. The voltage of thepulse is shown as one-half of the voltage V of the voltage source 44,while the time duration of the pulse is shown equal to twice the lengthl of the line H) divided by the velocity of the wave in the line, whichis a constant c for any given line. A mismatch would. result in aninitial pulse whose voltage is slightly more or less than one-half thevoltage of the voltage source 44, depending on the direction of themismatch, which initial pulse would be followed by additional pulses ofdiminishing vo1t- However, the total energy absorbed by the crystalwould remain the same, The energy absorbed by the crystal is found bytaking the square of one-half of the voltage of the voltage source 44,multiplied by the time duration of the pulse and dividing this by theimpedance of the crystal. This absorbed energy is usually expressed inergs.

After the cartridge-type crystal rectifier has been subjected to pulseenergy, other and known means are used to determine whether or not thecrystal has been impaired.

Thus it may be readily seen that a specified amount of energy may beimparted to a cartridge-type crystal rectifier in a specified time bythis invention by merely regulating the length l of the coaxial line andthe voltage V of the voltage source 44. It is further seen that thisenergy is applied with a minimum of contact chatter and mechanicalshock.

This invention is to be limited only by the appended claims.

What is claimed is:

1. Apparatus for applying pulse energy to an electrical devicecomprising, a transmission line, said transmission line comprising twoconductors and having a characteristic impedance substantially equal tothe impedance of said electrical device, one of said conductors of saidline being movably disposed relative to the other or said conductors,means for conductively connecting an electrical devce to one of saidconductors, a voltage source for charging said line, and means forrapidly moving said movable conductor in a direction to connectconductively said electrical device across said transmission line,whereby energy stored in said line is imparted to said electricaldevice.

2. Apparatus for applying pulse energy to an electrical devicecomprising, a transmission line, said line comprising two conductors,one of said conductors being movably disposed relative to the other ofsaid conductors, a voltage source for charging said line, means forconnecting an electrical device to one of said conductors in such amanner that when movement is imparted to said movable conductor saiddevice is connected across said line and the energy stored in said lineis imparted to said device, and means for moving said movable conductor.

3. Apparatus for applying pulse energy comprising a section of coaxialtransmission line of predetermined length, the inner conductor beingslidably disposed relative to the outer conductor, contact means mountedon said inner conductor, means mounted on said outer conductor adaptedto releasably connect a conductive electrical device to said outerconductor, means for electrically charging said coaxial line through aresistor carried by said inner condoctor, and means for rapidly movingsaid inner conductor to advance said contact means toward saidconnecting means mounted on said outer conductor, whereby an electricaldevice releasably connected to said outer conductor is conductivelyconnected across said line by said contact means and the energy storedin said line is imparted to said electrical device.

4. Apparatus comprising a section of coaxial line of predeterminedlength and of predetermined characteristic impedance, the innerconductor being movably disposed relative to the other conductor, meansfor charging said coaxial means for rapidly moving one conductorrelative to the other conductor, and means mounted on said conductoradapted to discharge the energy stored insaid line across an externalload upon movement of said one conductor.

5. Apparatus for applying pulse energy to an electrical devicecomprising a section of coaxial transmission line of predeterminedlength, the characteristic impedance of said line being equal to theimpedance of the electrical? device to which pulse energy is to beapplied, means for electrically charging said coaxial line, means formoving one conductor of said line relative to the other conductor ofsaid line, and means mounted on the conductors of said line adapted toimpart the electrical charge on said line to an electrical device uponmovement of one of said conductors.

6. Apparatus comprising a section of coaxial transmission line ofpredetermined length and predetermined characteristic impedance, meansmounted on one of said conductors adapted to releasably secure anelectrical device to said conductor, means for electrically chargingsaid mined length, the characteristic impedance of said line being equalto the impedance of the rectifier to which pulse energy is to beapplied, said coaxial line comprising an outer conductor and a slidableinner conductor, means for electrically charging said coaxial linethrough a resistor carried by said inner conductor, means for rapidlymoving said inner conductor relative to said outer conductor, and meanssecured to said conductors adapted to impart the electrical charge onsaid line to a cartridge type crystal rectifier upon movement of saidinner conductor.

8. Apparatus comprising an electrical device, a transmission line, saidtransmission line comprising two conductors and having a characteristieimpedance substantially equal to the impedance of said electricaldevice, one of said conductors of said line being movably disposedrelative to the other of said conductors, means for conductivelyXconnecting said electrical device to one of said conductors, a voltagesource for charging said line, and means for rapidly moving said movableconductor in a direction to connect conductively said electrical deviceacross said transmission line, whereby energy stored in said line isimparted to said electrical device.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,944,211 Brodie Jan. 23, 1934 2,108,637 Bartgis Feb. 15, 19382,255,898 Robb Sept. 16, 1941 2,406,405 Salisbury Aug. 2'7, 19462,407,847 Peterson Sept. 1'7, 1946 2,411,140 Lindenblad Nov. 12, 19462,459,849 Stateman Jan. 25, 1949

